1. Field of the Invention
The present invention relates to a spotter equipped with plural variable-pitch spotting heads to spot simultaneously, onto plural spotting positions arranged in an array, sample solutions collected from plural sample containers, respectively.
2. Description of the Related Art
In the development of array chips on which plural kinds of DNAs or proteins are placed, the sample solutions need to be spotted in an array within an area of several centimeters square on a substrate, such as a glass slide. Various automated spotter have been developed thus far for the purpose of carrying out the spotting to this end. Such an automated spotter includes, as its spotting heads, plural spotting heads including discharging portions, such as pins and pipette tips, and automatically carries out the following processes: collecting sample solutions from sample containers; then, spotting the solutions onto predetermined positions on a substrate; and, after that, washing the discharging portions, or disposing the discharging portions to replace them with unused discharging portions. Microtiter plates with 96 wells, 384 wells and 1536 wells are frequently-used examples of the sample containers. The wells of these Microtiter plates are arranged with arrays of 9 mm, 4.5 mm and 2.25 mm, respectively. On the other hand, when the spotting onto a substrate is carried out, the solutions are spotted at intervals ranging from several tens of micrometers to several hundreds of micrometers. Accordingly, in the spotting from sample containers, such as a Microtiter plate, onto a substrate, the array pitch of the spotting heads has to be changed in one way or another.
Conventional automated spotters are roughly classified into the following two groups. Each spotter of a first group includes plural variable-array spotting heads that are arranged along a straight line. Each spotter of the second group includes plural invariable-array spotting heads that are arranged in an array. The spotters of the first group employ pipette tips or needles as the discharging portions of their spotting heads. The minimum value of the array pitch of the spotting heads is restricted by the outer dimensions of each spotting head. Accordingly, the pitch varying mechanism is used only when the collecting and spotting of the sample solutions is performed between arrays of sample containers, such as Microtiter plates, having different array from each other (see Patent Documents 1, 2, 3 and 4). In spotting with a pitch smaller than the above case, each of the spotters carries out the spotting while shifting the spotting heads.
In spotting the sample solutions directly onto a substrate, the spotter spots one kind of sample solution by using one of the spotting heads at a time, and thus cannot achieve its full potential. The spotters of the second group employ pins as the discharging portions of their spotting heads, and the array of the spotting heads is not variable. Accordingly, the spotting heads of the spotter are formed with the same array as the Microtiter plate. The spotter carries out the spotting of the collected sample solutions to the due spotting positions simply by shifting the pitch (see Patent Documents 5 and 6).
As described above, conventional automated spotters are not designed for the purpose of spotting, directly onto a substrate, sample solutions collected from sample containers, and thus have the following problem. It takes a lot of time for such conventional automated spotters to carry out the spotting onto a single substrate. In addition, the more the total number of necessary spots becomes, the longer it takes for these spotters to finish spotting onto all the positions that need spotting. This problem, however, seems to be solved somewhat when the spotting is simultaneously carried out onto plural substrates so as to prepare plural substrates with identical spotting arrays, since time taken to spot samples on one substrate is relatively reduced. In contrast, for example, in the case of a small lot preparation of substrates, or in a case where the spotting array pitch needs to be changed frequently, the conventional automated spotters have no advantages. Accordingly, it is evident that the above-mentioned problem is left unsolved in its fundamental sense.    Patent Document 1: Japanese Patent Laid-Open No. H09-318636 (1997)    Patent Document 2: Japanese Patent Laid-Open No. H10-48100 (1998)    Patent Document 3. Japanese Patent Laid-Open No. 2003-315352    Patent Document 4: Japanese Patent Laid-Open No. 2005-91339    Patent Document 5: WO 95/35505    Patent Document 6: Japanese Patent Laid-Open No. H10-503841 (1998)